Principle:
The IR radiations from the object are detected and are converted into shades of gray. There shades of gray represent the temperature levels of the surface of the object over CRT screen.
Construction:
The IR camera consists of a plane mirror which is oscillating about a horizontal axis and an eight sided prism. Both can be rotated using motors.
The detector system is made of Indium antimonide which converts heat radiation into electrical signal. A separate cooling arrangement is made to cool the detector by placing liquid N2 into a dewar flask.
Working:
The IR radiation from the object is focused onto the oscillating plane mirror. This provides the vertical scanning of the object and the synchronized signal can be sent to display unit.(signal 1).
The image from the oscillating mirror is focused onto a rotating eight sided prism. This provides the horizontal scanning and the synchronized signals (signals 2) are sent to display unit.
These two signals (signal 1 and signal 2) produces an image of the object in the CRT display unit. The radiation from the eight sided prism is allowed to fall on the detector, after passing through the lens system.
Now the detector converts the IR radiation into electrical signals and is fed to the display unit after suitable amplification. The electrical signals produced depends on the energy of the incident radiation over the detector. Thus the signals modulate the beams intensity in the CRT display.
Thus the shades of gray of various intensity level is displayed in CRT. Each portion of gray (black and white) represents the various temperature of the object.
A digital display unit can be fixed below the CRT so that the temperature corresponding to any particular point of the object can be viewed directly.
Advantages:
1. It can be used to measure the temperature differences between any points of the object even upto 0.1oC.
2. Using colour display units we can find the temperature, with respect to the colours obtained on CRT.
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